Propellent powder and method for producing same



PROPELLENT POWDER AND METHOD FOR PRODUCING SAME John J. ONeill, Jr., Roxana, and Thomas F. McDonnell, Collinsville, 111., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Application December 17, 1952, Serial No. 326,588

4 Claims. (CI. 52-20) This invention relates to propellent powder and more particularly to novel disk-like propellent powder grains and their preparation.

The preparation of propellent powder by suspending and distributing globules of a propellent powder base lacquer throughout a non-solvent medium and solidifying the suspended lacquer globules by removal of the solvent so as to form individual spherical grains is well-known and is described in U. S. Patent 2,027,114 granted January 7, 1936 to Olsen, Tibbitts and Kerone. Heretofore,'when it was necessary to make disk-like powder for use in a particular ammunition load, an additional rolling operation was required on the finished powder. In accordance with such methods, disk-like propellent pow der grains were obtained from the spherical powder grains by passing them through a pair of calender rolls. Using this method, the powder may be rolled dry, in an aqueous slurry, or it may be softened prior to rolling as taught in U. S. Patent 2,111,075 granted March 15, 1938 to Olsen. While these processes yield desirable products, a number of steps are involved as well as additional apparatus.

More recently it has been discovered that the rolling of powder in an aqueous slurry introduces another variable into the process. As described in U. S. Patent 2,543,535 granted February 27, 1951 to Reichardt and Baldridge, the ballistic properties of the powder may be controlled by the amount of water at the time of rolling. While this process does provide a method of altering the ballistics of a powder, care must be exercised when roll ing powder to insure that the ballistic properties of two similar powder batches will not be changed by a variation in the length of time they are maintained in the slurry prior to rolling. The manufacture of flake powder from spherical powder grains thus involves the preparation of the globular powder grains in accordance with 'U. S. Patent 2,027,114, followed by removal of the charge from the grain-forming apparatus, washing and screening the powder, forming an aqueous slurry of the powder grains and finally rolling and drying them. Furthermore, such a rolling process is completely unsatisfactory in the preparation of low density propellent powder because a very large percentage of such grains are split or even completely reduced to a fine dust by the pressure of the rolls and thus rendered useless.

An object of this invention is therefore to provide a method of preparing disk-like powder that eliminates such disadvantages of prior processes. Another object of this invention is to eliminate the rolling step in the prepara tion of disk-like propellent powder. Another object is to provide a new improved powder grain. Another object is to provide a novel process for the preparation of propellent powder. A more specific object of this invention nited States Patent ice " mechanical agitation in excess of that required to maintain the particles suspended in the non-solvent medium, i. e., more than that necessary to result in the formation of spheres. The normal expectation from the application of such additional mechanical energy would be a breaking up of the particles of lacquer into very small units and the formation of irregular shapes and the like, as might be inferred from the disclosure in the aforementioned U. S. Patent 2,027,114. It has been found, instead, that the resulting particles obtained are uniformly disk-like in shape and that the ratio of their minor axis to their major axis is between about 0.3 and about 0.6, with a substantially complete absence of irregular shaped particles. That the fluid lacquer particles would uniformly assume such disk-like shape, when surtional energy are generally required to be applied to systems with decreasing ratios of amounts of non-solvent medium to amounts of lacquer particles, and the reverse is true, namely, greater amounts of additional energy must be applied to the system when the ratio of non solvent medium to lacquer is increased. The introduction of greater amounts of additional mechanical energy to systems containing smaller amounts of propellent pow der base lacquer is believed to be necessary because the percentage of the energy introduced into the system actu ally applied to the suspended lacquer particles varies more or less directly with the amount of lacquer dispersed in the non-solvent medium, Whereas considerable latitude maybe exercised with respect to the amount of additional energy for a particular ratio of non-solvent medium to lacquer, in general it is preferred that the amount of energy applied be at least 15% greater than that essential for suspension of the particles with nonsolvent medium to lacquer ratios in the range, say, from about 1.2:1 to 20:1. A preferred ratio from a practical handling standpoint is from about 1.2 to about 1.7 parts by volume non-solvent medium per part of lacquer. For eitective operation it is desirable that the additional energy applied to the lacquer particles themselves be equal to or greater than that required to overcome the interfacial tension of the lacquer surface, say about 2.6 dynes per square centimeter with the usual lacquer. 'In a process for forming spherical grains of powder, as

forinstance described i n U.-S. Patent 2,027,114, the amount Of'energYaP Iied-to the'systetn by means of agitation is always less than that essential in accordance ith as in st n In carrying out the process in accordance with this invention the powder base, solvent, and non-solvent medium may be assembled or brought together in any desired sequence to eifect solution of the powder base with the incorporation thereof in the non-solvent medium. After such solution is substantially complete a protective colloid s added o the sy tem an qn r ltsd i at on is th n applied to determine the exact particle size of the powder grain, with smaller particle sizes being obtained with more violent agitation, as .is well known in the art. After the lacquer has been broken up into particles of the desired S z t o en s em v d from the part cles; a h Pa t s a sha ed. pr o to and d r t solven removal process by applying the additional mechanical ns t h S m b mea s f a it t o a described n he q s o a A o gh a y ui bl y of i a n mechanism may be employed which will maintain the P r s n e s pen i t s Pr a e o use a mor Simple t ne of ppa a u n w i h t a itato d s fo e am amount t ev l paddl or t ke- The invention will be further clarified and more easily understood in view of the following embodiments, which exem y practic s th .may e ollow d in ca y ou the process of this invention. All proportions are expressed as parts by weight unless otherwise indicated.

The process may be conveniently carried out in a single vessel provided with the necessary facilities, such as means for heating and cooling the contents, for example a suitable jacket through which cooling or heating fluid may be circulated; suitable means for agitation, such as a rotatable shaft on which are mounted a plurality of horizontally disposed blades, the action of which may be supplemented by baffles which project inwardly from the sides of the vessel; an orifice at the top for charging the vessel and a cover for sealing the same; an outlet at the bottom of the vessel for discharging the contents and a suitable valve for opening and closing the same; and a vapor outlet leading to a condenser furnished with a valve that may be opened or closed at will.

Four hundred and fifty (450) parts of water, 6 0 parts of finely divided uncolloided nitrocellulose with a viscosity (Hercules Method) in the neighborhood of 6 to 10 seconds, and 0.15 part .of powdered chalk were added to a vessel of the above type This mixture was violently agitated by rotating the agitator at asuflicient rate (e. g., approximately 140 R. P. M. .at a radius of about l112 inches in a vessel about 30 inches in diameter) so that the contents were in a turbulent'state and the nitrocellulose wasdis'tribut ed substantially uniformly throughout the water." The agitation was maintained during the entire process. Two hundred and twenty-two (222) parts of ethyl acetate containing 0.45 part of dissolved diphenylamiue were then added to the agitated mixture of water and nitrocellulose, and the contents of the vessel were heated to about 68 C. over a period of approximately two hours. At the end of this heating period, the nitrocellulose had substantially dissolved in the ethyl acetate to form 'nc'indescripi particles'of nitrocellulose lacquer suspended'in the water. Three parts of animal glue dissolved in 30 parts of water were added to the contents of the vessel, and the lacquer separated into a multitude of relatively uniformly sized, but irregular shaped particles, each of which was destined to be a grain of smokeless powder upon removal of the ethyl acetate. At the end of this period the aqueous suspension of lacquer particles was gradually heated from 68: C. to about 99 C. in order to remove the ethyl acetate from the system, thus solidifying each particle of suspended nitrocellulose into a grain of propellent powder. After removal of the solvent the suspension was allowed to cool, the agitator was stopped and the powder grains were recovered by filtrationand washed with warm water to remove the protectivfi colloid. The grains may then be subjected to a screening operation for separating the over-sized and undersized grains from the product. In this "iafil iwhe""continued"agrarian$ R 'P. M. supplied suificient energy to the system to provide the disk-like shape to the lacquer particles. Another batch of powder prepared in substantially the same manner, but agitated at only 70 R. P. M. after the lacquer had been dispersed throughout the water, was composed of grains of spherical powder and no disk shaped grains were found therein.

The grains thus formed, while not uniform in size, exhibited a striking consistency in the ratio of minor to major axes. That." this ratio is maintained within close limits is clearly illustrated "in the following table, where W is the minor axis or web, D is the major axis or diameter, and W/D, the ratio of the former to the latter.' In each instance the values are "gi'ven'i'n inches.

W D W/D any process involving the solidification of disk-like parti-- cles of a powder base lacquer suspended in a non-solvent. Water is, of course, the most economical non-solvent medium, and solvents such as ethyl acetate, methyl ethyl ketone, and isopropyl acetate are advantageously used in conjunction with it. The invention is also applicable to other smokeless powder bases such as nitro-cellulose and accelerators, nitrocellulose and deterrents, nitro-cellulosenitroglycerine with deterrents, as well as other similar gelatinizable polynitro compounds, for instance nitro-starch and polyvinyl nitrate. Also the powder bases entering the process may be either gelatinized or ungelatinlzed. It is to be distinctly understood, therefore, that various modifications or variations may be made without departing from the spirit and scope of this invention. I

Having thus described the invention, what is claimed 1. In the art of making explosives by a process which comprises agitating particles of a propellent powder base q r in a ent medium in th PI 9 a protective colloid and removing solvent from sa d particles by heating while maintaining the suspension '1I1 said medium, the step offorming disk powder grains by applying to said particles in suspension agitation at least 15% in excess of that required to maintain them suspended in the medium, while maintainingithe' ratio of.

non-solvent medium to lacguer between about 2.021 and about 1.2:1, and removing the solventfrom particles during the application of said agitation? 2. Theprocess of elairn l in which the ratio of nonsolvent medium to propellent base lacquer is between about 1.2:1 and about 1.7:1.

3. LA disk shaped smokeless powder base propellent grain having a web from about.( 3 to about 0.6 ofthe iame e cf the sta andl vias a wnt n o eelau surface,

2,787,538 5 6 4. In the art of making explosives by a process which 1.2:1, and removing the solvent from said particles during comprises agitating particles of a propellant powder base the application of said agitation.

lacquer in a non-solvent medium in the presence of a protective colloid and removing solvent from said particles References cued m the file of thls Pawnt by heating While maintaining the suspension in said 5 UNITED STATES PATENTS medium, the step of forming disk p w r gr n y pply 2,027,114 Olsen et al Jan. 7, 1936 ing to said particles in suspension agitation about 100 2,247,392 Lindsley July 1, 1941 percent in excess of that required to maintain them sus- 2,344,516 McBride Mar. 21, 1944 pended in the medium, while maintaining the ratio of 2,375,175 Silk May 1, 1945 non-solvent medium to lacquer between about 2.021 and 10 2,575,871 Gordon et al. Nov. 20, 1951 

1. IN THE ART OF MAKING EXPLOSIVES BY A PROCESS WHICH COMPRISES AGITATING PARTICLES OF A PROPELLENT POWDER BASE LACQUER IN A NON-SOLVENT MEDIUM IN THE PRESENCE OF A PROTECTIVE COLLOID AND REMOVING SOLVENT FROM SAID PARTICLES BY HEATING WHILE MAINTAINING THE SUSPENSION IN SAID MEDIUM, THE STEP OF FORMING DISK POWEDER GRAINS BY APPLYING TO SAID PARTICLES IN SUSPENSION AGITATION AT LEAST 15% IN EXCESS OF THE REQUIRED TO MAINTAIN THEM SUSPENDED IN THE MEDIUM, WHILE MAINTAINING THE RATIO OF NON-SOLVENT MEDIUM TO LACQUER BETWEEN ABOUT 2.0:1 AND ABOUT 1.2:1, AND REMOVING THE SOLVENT FROM SAID PARTICLES DURING THE APPLICATION OF SAID AGITATION. 